function split (s, splitter)
  result = {};
  for match in (s..splitter):gmatch("(.-)"..splitter) do
      table.insert(result, match);
  end
  return result;
end

function setBalance(username, password, balance)
  local file = fs.open("/data/"..username,"w")
  --Rewrite password and balance
  file.writeLine(password)
  file.writeLine(balance)
end

function getBalance(username)
  local file = fs.open("/data/"..username,"r")
  --We only want the second line
  file.readLine()
  return file.readLine()
end

function verify(username, password)
  if fs.exists("/data/"..username) == false then
    return "404";
  else
    --the user exists
    local file = fs.open("/data/"..username,"r")
    if password == file.readLine() then
      --correct password
      return "0";
    else
      --incorrect password
      return "403";
    end
  end
end
local modem = peripheral.wrap("top")

textutils.slowPrint("Starting Server...")

while true do
  modem.open(1)

  local _, side, freq, rfreq, message = os.pullEvent("modem_message")
  msg = split(message, "`")
  for key, value in pairs(msg) do
    if key == 1 then
      action = value
    elseif key == 2 then
      var1 = value
    elseif key == 3 then
      var2 = value
    elseif key == 4 then
      var3 = value
    elseif key == 5 then
      var4 = value
    end
  end
  if fs.exists("/data") == false then
    fs.makeDir("/data")
  end
  --Do the requested action
  if action == "balance" then
    user = verify(var1, var2)
    if user == "0" then
      --Give balance
      modem.transmit(1,1,getBalance(var1))
    elseif user == "403" then
      print("Failed login attempt for user "..var1)
      modem.transmit(1,1,"403")
    elseif user == "404" then
      print("Non existant "..var1.." just tried to login")
      modem.transmit(1,1,"404")
    end
  elseif action == "register" then
    --Checking if the user exists
    if verify(var1,"") == "404" then
      --its a new user!
      local file = fs.open("/data/"..var1,"a")
      file.writeLine(var2)
      file.writeLine("0")
      file.close()
      modem.transmit(1,1,"0")
      print("Registered user "..var1)
    else
      --user already exists
      modem.transmit(1,1,"409")
    end
  elseif action == "pay" then
    --User wants to pay another user
    --var1 is the user that wants to pay
    --var2 is the users password
    --var3 is the user that is being paid
    --var4 is the amount that is being processed
    print(var1.." paid "..var3.." $"var4)
    --Check they have the correct password
    local file = fs.open("/data/"..var1,"r")
    pass = file.readLine()
    balance = file.readLine()
    file.close()
    newBalance = tonumber(balance) - var4
    if newBalance > 0 then
      --User has enough money
      if pass == var2 then
        --Authenticated
        setBalance(var1,var2,newBalance)
        local file = fs.open("/data/"..var1,"r")
        payeePassword = file.readLine()
        payeeBalance = file.readLine()
        setBalance(payee, payeePassword, tonumber(payeeBalance) + amount)
      end
    end
  end
end